Recently, a large scale storage system, in which data is distributed and recorded in a large number of information processing terminals interconnected over a network. In this distributed storage system, a server for recording and managing data transmits data to information processing terminals or to other servers, by e.g. multi-cast, for recording on local recording mediums provided in the information processing terminals or other servers.
If, in this case, data is to be taken out on demand, a large amount of data must be recorded in the recording medium. For example, if data is a motion picture, with the data capacity of approximately 2 Gbytes, and 500 of such motion pictures are to be recorded, the capacity not less than 1 terabyte is needed.
On the other hand, if, as an example of providing data by streaming, the server provides data to a client which requests the data by uncast, a protocol is used, in which re-transmission of data, such as an arrival complete signal (ACK signal) of TCP/IP, is requested for achieving error-free transmission.
However, this technique imposes significant load on the server, so that, in the current status of the art, services can be rendered to only hundreds of clients even if a high performance server is used. Even if a protocol, not employing the ACK, such as UDP/IP, is used, the number of clients, to whom services can be rendered, is not more than the order of thousands. Thus, if it is tried to provide data by streaming, server side costs are raised, such that the number of the clients is limited.
Recently, such a system has been proposed in which FEC (Forward Error Correction) is used as a multi-cast technique and in which data is transmitted to plural clients without requesting re-transmission of data. This system is such a one in which a server repeatedly transmits a stream by multi-cast and in which a client picks up necessary signals form the stream and decodes and reproduces the so picked up data.
In transmitting picture data of 500 motion pictures, each amounting to 2 Gbytes, within ten minutes, a transmission bandwidth of approximately 14.7 Gbits/sec is needed. If the same amount of the picture data is to be transmitted within one minute, the transmission bandwidth of approximately 147 Gbits/sec is needed. Although the above numerical values are theoretical values, the server that is able to withstand the capacity or the transmission system is extremely costly and, if such server is built, it is not practical. Although there is such a system in which data is distributed and recorded in a plural number of hosts, such a system is in need of increased processing for data management or data communication, because a huge amount of data has to be managed by plural servers.